This invention relates to a gas turbine aircraft engine, and more particularly, to an air inlet assembly that uses an inertial separator effect to prevent the entry of water and other debris into the air intake of such an engine.
The inertial separation effect has been widely employed to prevent ingress to an aircraft engine of water particles, ice, snow, and other debris carried by the airstream passing through the inlet air duct. The effect is typically obtained through the use of an air-deflecting door that is hinged to a wall of the air duct upstream of an opening through that wall into the plenum that surrounds the engine air inlet. In normal conditions, the hinged door is positioned against the wall so that the air duct is opened. In the presence of debris, i.e., under the so-called "icing conditions", the door is pivoted away from the wall and across a portion of the air duct to confine the incoming air to a passage of reduced cross section. As the incoming air passes through this reduced area, it is accelerated. Since the accelerated particles of debris have a higher inertia than the carrier airstream, these particles are unable to make the sharp turn needed to reach the engine inlet, i.e., around the trailing edge of the door and through the opening into the plenum. Thus, the accelerated particles pass freely through an unimpeded path to the air duct outlet further downstream. U.S. Pat. No. 3,329,377 to Peterson et al. is an example of this type of inertial separator.
When the deflector door of the above-described arrangement is extended in the anti-icing mode, there is a significant loss of pressure between the exit plane across the trailing edge of the door and the engine plenum. There is, accordingly, a significant reduction in the recovery of the pressure of the slipstream generated by the propeller, i.e., a reduction in the so-called "ram recovery." To compensate for this pressure loss, Tedstone et al. in U.S. Pat. No. 3,952,972 added a fairing to the trailing edge of the deflector door. When the door is in the extended position in the Tedstone et al. arrangement, the curved fairing smoothes the flow of the portion of the incoming airstream that is directed into the plenum. When the door is retracted, however, the positioning of the curved fairing in the plenum opening tends to disrupt the flow into the engine air intake, thus reducing ram recovery.
To overcome the disadvantages of the above-described door-plus-fairing arrangement, Tedstone, in U.S. Pat. No. 4,346,860, developed an air duct assembly in which the earlier straight trailing edge deflecting door is combined with a fixed fairing that is attached to and extends between the sidewalls of the air duct. In the icing mode, the straight trailing edge of the door fits against the leading edge of the vane, thus reducing the cross section of the air duct to achieve the inertial separation effect. The fixed fairing provides a low-pressure surface that functions like the earlier fairing to turn a portion of the incoming air toward the engine inlet. Since the fixed fairing has an airfoil shape, it continues to function as a turning vane when the deflecting door is returned to its position against the wall of the air duct. The surface of the fixed vane that turns the flow in the anti-icing mode has a convex central portion that merges with flat surfaces that extend to the leading and trailing edges. While this arrangement does provide improved recovery of pressure in the nonicing mode, losses remain, owing in part to the configuration of the vane and in part to the presence at the plenum inlet of the abrupt straight edge of the retracted deflector door.
The present invention provides an improved arrangement that overcomes the disadvantages of the developments described above. In particular, an important aspect of the invention is the provision of an optimized fixed turning vane that functions both in the anti-icing and normal modes to direct air toward the engine inlet. A further aspect of the invention is the provision of a turning vane on the trailing edge of the air deflector door which, in the normal mode, cooperates with the fixed turning vane to form an aerodynamic converging channel for accelerating the flow in a smooth, attached manner into the engine air intake area.